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Re: [patch tree-optimization]: allow branch-cost optimization for truth-and/or on mode-expanded simple boolean-operands


On Fri, Oct 21, 2011 at 2:19 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
> 2011/10/21 Richard Guenther <richard.guenther@gmail.com>:
>> On Thu, Oct 20, 2011 at 3:08 PM, Kai Tietz <ktietz@redhat.com> wrote:
>>> Hello,
>>>
>>> this patch re-enables the branch-cost optimization on simple boolean-typed operands, which are casted to a wider integral type. ?This happens due casts from
>>> boolean-types are preserved, but FE might expands simple-expression to wider mode.
>>>
>>> I added two tests for already working branch-cost optimization for IA-architecture and
>>> two for explicit checking for boolean-type.
>>>
>>> ChangeLog
>>>
>>> 2011-10-20 ?Kai Tietz ?<ktietz@redhat.com>
>>>
>>> ? ? ? ?* fold-const.c (simple_operand_p_2): Handle integral
>>> ? ? ? ?casts from boolean-operands.
>>>
>>> 2011-10-20 ?Kai Tietz ?<ktietz@redhat.com>
>>>
>>> ? ? ? ?* gcc.target/i386/branch-cost1.c: New test.
>>> ? ? ? ?* gcc.target/i386/branch-cost2.c: New test.
>>> ? ? ? ?* gcc.target/i386/branch-cost3.c: New test.
>>> ? ? ? ?* gcc.target/i386/branch-cost4.c: New test.
>>>
>>> Bootstrapped and regression tested on x86_64-unknown-linux-gnu for all languages including Ada and Obj-C++. ?Ok for apply?
>>>
>>> Regards,
>>> Kai
>>>
>>> Index: gcc-head/gcc/testsuite/gcc.target/i386/branch-cost2.c
>>> ===================================================================
>>> --- /dev/null
>>> +++ gcc-head/gcc/testsuite/gcc.target/i386/branch-cost2.c
>>> @@ -0,0 +1,16 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2 -fdump-tree-gimple -mbranch-cost=2" } */
>>> +
>>> +extern int doo (void);
>>> +
>>> +int
>>> +foo (int a, int b)
>>> +{
>>> + ?if (a && b)
>>> + ? return doo ();
>>> + ?return 0;
>>> +}
>>> +
>>> +/* { dg-final { scan-tree-dump-times "if " 1 "gimple" } } */
>>> +/* { dg-final { scan-tree-dump-times " & " 1 "gimple" } } */
>>> +/* { dg-final { cleanup-tree-dump "gimple" } } */
>>> Index: gcc-head/gcc/testsuite/gcc.target/i386/branch-cost3.c
>>> ===================================================================
>>> --- /dev/null
>>> +++ gcc-head/gcc/testsuite/gcc.target/i386/branch-cost3.c
>>> @@ -0,0 +1,16 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2 -fdump-tree-gimple -mbranch-cost=2" } */
>>> +
>>> +extern int doo (void);
>>> +
>>> +int
>>> +foo (_Bool a, _Bool b)
>>> +{
>>> + ?if (a && b)
>>> + ? return doo ();
>>> + ?return 0;
>>> +}
>>> +
>>> +/* { dg-final { scan-tree-dump-times "if " 1 "gimple" } } */
>>> +/* { dg-final { scan-tree-dump-times " & " 1 "gimple" } } */
>>> +/* { dg-final { cleanup-tree-dump "gimple" } } */
>>> Index: gcc-head/gcc/testsuite/gcc.target/i386/branch-cost4.c
>>> ===================================================================
>>> --- /dev/null
>>> +++ gcc-head/gcc/testsuite/gcc.target/i386/branch-cost4.c
>>> @@ -0,0 +1,16 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2 -fdump-tree-gimple -mbranch-cost=0" } */
>>> +
>>> +extern int doo (void);
>>> +
>>> +int
>>> +foo (_Bool a, _Bool b)
>>> +{
>>> + ?if (a && b)
>>> + ? return doo ();
>>> + ?return 0;
>>> +}
>>> +
>>> +/* { dg-final { scan-tree-dump-times "if " 2 "gimple" } } */
>>> +/* { dg-final { scan-tree-dump-not " & " "gimple" } } */
>>> +/* { dg-final { cleanup-tree-dump "gimple" } } */
>>> Index: gcc-head/gcc/fold-const.c
>>> ===================================================================
>>> --- gcc-head.orig/gcc/fold-const.c
>>> +++ gcc-head/gcc/fold-const.c
>>> @@ -3706,6 +3706,19 @@ simple_operand_p_2 (tree exp)
>>> ? /* Strip any conversions that don't change the machine mode. ?*/
>>> ? STRIP_NOPS (exp);
>>>
>>> + ?/* Handle integral widening casts from boolean-typed
>>> + ? ? expressions as simple. ?This happens due casts from
>>> + ? ? boolean-types are preserved, but FE might expands
>>> + ? ? simple-expression to wider mode. ?*/
>>> + ?if (INTEGRAL_TYPE_P (TREE_TYPE (exp))
>>> + ? ? ?&& CONVERT_EXPR_P (exp)
>>> + ? ? ?&& TREE_CODE (TREE_TYPE (TREE_OPERAND (exp, 0)))
>>> + ? ? ? ?== BOOLEAN_TYPE)
>>> + ? ?{
>>> + ? ? ?exp = TREE_OPERAND (exp, 0);
>>> + ? ? ?STRIP_NOPS (exp);
>>> + ? ?}
>>> +
>>
>> Huh, well. ?I think the above is just too special and you instead should
>> replace the existing STRIP_NOPS by
>>
>> while (CONVERT_EXPR_P (exp))
>> ?exp = TREE_OPERAND (exp, 0);
>>
>> with a comment that conversions are considered simple.
>>
>> Ok with that change, if it bootstraps & tests ok.
>>
>> Richard.
>
> Ok, bootstrapped and regression-tested on x86_64-unknown-linux-gnu and
> applied to trunk with modifying as you suggested.
>
> One question I have about handling of TRUTH-binaries in general in
> fold-const.c. ?Why aren't we enforcing already here in fold_binary for
> those operations, that operands get boolean-type? ?I see here some
> advantages of C-AST folding. ?I've tested it and saw that even later
> in SSA-passes we get slightly better results on that.

Because we do not want to mess with the Frontends AST.

Richard.

> Regards,
> Kai
>


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